This invention regards a loading pipe in the cargo pressure tank of a ship. In particular, it concerns a pipe placed inside a cargo pressure tank, wherein the pipe is arranged especially for use during loading and unloading of the ship.
Sea transport of gaseous petroleum products has taken place mainly by means of the so-called Liquefied Natural Gas (LNG) method. The method includes cooling of gas to a liquid state, whereupon the gas may be transported in ship tanks at atmospheric pressure. Costly equipment is required both at the location of shipment and at the receiving end. As the gas must be cooled to a relatively low temperature, up to a fifth of the gas is used for operation of the cooling and heating processes. Consuming this amount of energy solely for transport-related processes is expensive and also environmentally questionable.
Several other ship-based solutions have been proposed, in which the gas is pressurised and/or cooled in order to attain a gas density that is practical for the purpose. Such solutions have gained little practical use, but a solution in which a large number of vertical tubular pressure tanks are placed in the cargo hold of a ship, has attracted considerable attention. The method is termed Pressurised Natural Gas—PNG. According to such a method, the gas is compressed at the shipment site to an overpressure of a couple of hundred bars, and then is filled onto the cargo pressure tanks located on the ship. The cooling is limited to a simple and inexpensive removal of the compression heat from the gas, the transport temperature thus becoming close to the ambient temperature.
When using a relatively large number of preferably vertically mounted cargo pressure tanks in the hold of the ship, it is desirable for each cargo pressure tank to have as few pipe connections as possible. Pipe connections subjected to high pressure during loading, transport and unloading should be monitored continuously.
Essentially, the pipework of the ship must allow complete emptying of the cargo pressure tank. Moreover, it must be designed so as to allow easy inspection of the external pipe connections on the cargo pressure tank.